This is the perfect pet to use against Eleanor, in your garrison dailies. Toss up your shield in round 1 (blocks the big attack), then stampede & flurry. Two level 23 rats easily took out this undead goat. Simple!

Snowfall Alcove is abundant with these critters. Don't waste your time trying to find a rare Frostfur Rat as a secondary pet to something like an Icespine Hatchling, for instance. Go directly to Snowfall Alcove and surrounding areas and you'll find them at the bases of the trees.

These do come as a main pet and a secondary with other pets in the area. If you farm Icespine Hatchlings for leveling purposes you can find a rare rat pretty fast. I found mine not even looking for it. :)